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                                <h1 id="&#x6570;&#x636E;&#x7C7B;&#x578B;&#x6982;&#x8FF0;">&#x6570;&#x636E;&#x7C7B;&#x578B;&#x6982;&#x8FF0;</h1>
<h2 id="&#x7B80;&#x4ECB;">&#x7B80;&#x4ECB;</h2>
<p>JavaScript &#x8BED;&#x8A00;&#x7684;&#x6BCF;&#x4E00;&#x4E2A;&#x503C;&#xFF0C;&#x90FD;&#x5C5E;&#x4E8E;&#x67D0;&#x4E00;&#x79CD;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x3002;JavaScript &#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x5171;&#x6709;&#x516D;&#x79CD;&#x3002;&#xFF08;ES6 &#x53C8;&#x65B0;&#x589E;&#x4E86;&#x7B2C;&#x4E03;&#x79CD; Symbol &#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x672C;&#x6559;&#x7A0B;&#x4E0D;&#x6D89;&#x53CA;&#x3002;&#xFF09;</p>
<ul>
<li>&#x6570;&#x503C;&#xFF08;number&#xFF09;&#xFF1A;&#x6574;&#x6570;&#x548C;&#x5C0F;&#x6570;&#xFF08;&#x6BD4;&#x5982;<code>1</code>&#x548C;<code>3.14</code>&#xFF09;</li>
<li>&#x5B57;&#x7B26;&#x4E32;&#xFF08;string&#xFF09;&#xFF1A;&#x6587;&#x672C;&#xFF08;&#x6BD4;&#x5982;<code>Hello World</code>&#xFF09;&#x3002;</li>
<li>&#x5E03;&#x5C14;&#x503C;&#xFF08;boolean&#xFF09;&#xFF1A;&#x8868;&#x793A;&#x771F;&#x4F2A;&#x7684;&#x4E24;&#x4E2A;&#x7279;&#x6B8A;&#x503C;&#xFF0C;&#x5373;<code>true</code>&#xFF08;&#x771F;&#xFF09;&#x548C;<code>false</code>&#xFF08;&#x5047;&#xFF09;</li>
<li><code>undefined</code>&#xFF1A;&#x8868;&#x793A;&#x201C;&#x672A;&#x5B9A;&#x4E49;&#x201D;&#x6216;&#x4E0D;&#x5B58;&#x5728;&#xFF0C;&#x5373;&#x7531;&#x4E8E;&#x76EE;&#x524D;&#x6CA1;&#x6709;&#x5B9A;&#x4E49;&#xFF0C;&#x6240;&#x4EE5;&#x6B64;&#x5904;&#x6682;&#x65F6;&#x6CA1;&#x6709;&#x4EFB;&#x4F55;&#x503C;</li>
<li><code>null</code>&#xFF1A;&#x8868;&#x793A;&#x7A7A;&#x503C;&#xFF0C;&#x5373;&#x6B64;&#x5904;&#x7684;&#x503C;&#x4E3A;&#x7A7A;&#x3002;</li>
<li>&#x5BF9;&#x8C61;&#xFF08;object&#xFF09;&#xFF1A;&#x5404;&#x79CD;&#x503C;&#x7EC4;&#x6210;&#x7684;&#x96C6;&#x5408;&#x3002;</li>
</ul>
<p>&#x901A;&#x5E38;&#xFF0C;&#x6570;&#x503C;&#x3001;&#x5B57;&#x7B26;&#x4E32;&#x3001;&#x5E03;&#x5C14;&#x503C;&#x8FD9;&#x4E09;&#x79CD;&#x7C7B;&#x578B;&#xFF0C;&#x5408;&#x79F0;&#x4E3A;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#xFF08;primitive type&#xFF09;&#x7684;&#x503C;&#xFF0C;&#x5373;&#x5B83;&#x4EEC;&#x662F;&#x6700;&#x57FA;&#x672C;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x4E0D;&#x80FD;&#x518D;&#x7EC6;&#x5206;&#x4E86;&#x3002;&#x5BF9;&#x8C61;&#x5219;&#x79F0;&#x4E3A;&#x5408;&#x6210;&#x7C7B;&#x578B;&#xFF08;complex type&#xFF09;&#x7684;&#x503C;&#xFF0C;&#x56E0;&#x4E3A;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x5F80;&#x5F80;&#x662F;&#x591A;&#x4E2A;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x7684;&#x5408;&#x6210;&#xFF0C;&#x53EF;&#x4EE5;&#x770B;&#x4F5C;&#x662F;&#x4E00;&#x4E2A;&#x5B58;&#x653E;&#x5404;&#x79CD;&#x503C;&#x7684;&#x5BB9;&#x5668;&#x3002;&#x81F3;&#x4E8E;<code>undefined</code>&#x548C;<code>null</code>&#xFF0C;&#x4E00;&#x822C;&#x5C06;&#x5B83;&#x4EEC;&#x770B;&#x6210;&#x4E24;&#x4E2A;&#x7279;&#x6B8A;&#x503C;&#x3002;</p>
<p>&#x5BF9;&#x8C61;&#x662F;&#x6700;&#x590D;&#x6742;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x53C8;&#x53EF;&#x4EE5;&#x5206;&#x6210;&#x4E09;&#x4E2A;&#x5B50;&#x7C7B;&#x578B;&#x3002;</p>
<ul>
<li>&#x72ED;&#x4E49;&#x7684;&#x5BF9;&#x8C61;&#xFF08;object&#xFF09;</li>
<li>&#x6570;&#x7EC4;&#xFF08;array&#xFF09;</li>
<li>&#x51FD;&#x6570;&#xFF08;function&#xFF09;</li>
</ul>
<p>&#x72ED;&#x4E49;&#x7684;&#x5BF9;&#x8C61;&#x548C;&#x6570;&#x7EC4;&#x662F;&#x4E24;&#x79CD;&#x4E0D;&#x540C;&#x7684;&#x6570;&#x636E;&#x7EC4;&#x5408;&#x65B9;&#x5F0F;&#xFF0C;&#x9664;&#x975E;&#x7279;&#x522B;&#x58F0;&#x660E;&#xFF0C;&#x672C;&#x6559;&#x7A0B;&#x7684;&#x201C;&#x5BF9;&#x8C61;&#x201D;&#x90FD;&#x7279;&#x6307;&#x72ED;&#x4E49;&#x7684;&#x5BF9;&#x8C61;&#x3002;&#x51FD;&#x6570;&#x5176;&#x5B9E;&#x662F;&#x5904;&#x7406;&#x6570;&#x636E;&#x7684;&#x65B9;&#x6CD5;&#xFF0C;JavaScript &#x628A;&#x5B83;&#x5F53;&#x6210;&#x4E00;&#x79CD;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x53EF;&#x4EE5;&#x8D4B;&#x503C;&#x7ED9;&#x53D8;&#x91CF;&#xFF0C;&#x8FD9;&#x4E3A;&#x7F16;&#x7A0B;&#x5E26;&#x6765;&#x4E86;&#x5F88;&#x5927;&#x7684;&#x7075;&#x6D3B;&#x6027;&#xFF0C;&#x4E5F;&#x4E3A; JavaScript &#x7684;&#x201C;&#x51FD;&#x6570;&#x5F0F;&#x7F16;&#x7A0B;&#x201D;&#x5960;&#x5B9A;&#x4E86;&#x57FA;&#x7840;&#x3002;</p>
<h2 id="typeof-&#x8FD0;&#x7B97;&#x7B26;">typeof &#x8FD0;&#x7B97;&#x7B26;</h2>
<p>JavaScript &#x6709;&#x4E09;&#x79CD;&#x65B9;&#x6CD5;&#xFF0C;&#x53EF;&#x4EE5;&#x786E;&#x5B9A;&#x4E00;&#x4E2A;&#x503C;&#x5230;&#x5E95;&#x662F;&#x4EC0;&#x4E48;&#x7C7B;&#x578B;&#x3002;</p>
<ul>
<li><code>typeof</code>&#x8FD0;&#x7B97;&#x7B26;</li>
<li><code>instanceof</code>&#x8FD0;&#x7B97;&#x7B26;</li>
<li><code>Object.prototype.toString</code>&#x65B9;&#x6CD5;</li>
</ul>
<p><code>instanceof</code>&#x8FD0;&#x7B97;&#x7B26;&#x548C;<code>Object.prototype.toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5C06;&#x5728;&#x540E;&#x6587;&#x4ECB;&#x7ECD;&#x3002;&#x8FD9;&#x91CC;&#x4ECB;&#x7ECD;<code>typeof</code>&#x8FD0;&#x7B97;&#x7B26;&#x3002;</p>
<p><code>typeof</code>&#x8FD0;&#x7B97;&#x7B26;&#x53EF;&#x4EE5;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x503C;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x3002;</p>
<p>&#x6570;&#x503C;&#x3001;&#x5B57;&#x7B26;&#x4E32;&#x3001;&#x5E03;&#x5C14;&#x503C;&#x5206;&#x522B;&#x8FD4;&#x56DE;<code>number</code>&#x3001;<code>string</code>&#x3001;<code>boolean</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> <span class="hljs-comment">// &quot;number&quot;</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-string">&apos;123&apos;</span> <span class="hljs-comment">// &quot;string&quot;</span>
<span class="hljs-keyword">typeof</span> <span class="hljs-literal">false</span> <span class="hljs-comment">// &quot;boolean&quot;</span>
</code></pre>
<p>&#x51FD;&#x6570;&#x8FD4;&#x56DE;<code>function</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">f</span>(<span class="hljs-params"></span>) </span>{}
<span class="hljs-keyword">typeof</span> f
<span class="hljs-comment">// &quot;function&quot;</span>
</code></pre>
<p><code>undefined</code>&#x8FD4;&#x56DE;<code>undefined</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">typeof</span> <span class="hljs-literal">undefined</span>
<span class="hljs-comment">// &quot;undefined&quot;</span>
</code></pre>
<p>&#x5229;&#x7528;&#x8FD9;&#x4E00;&#x70B9;&#xFF0C;<code>typeof</code>&#x53EF;&#x4EE5;&#x7528;&#x6765;&#x68C0;&#x67E5;&#x4E00;&#x4E2A;&#x6CA1;&#x6709;&#x58F0;&#x660E;&#x7684;&#x53D8;&#x91CF;&#xFF0C;&#x800C;&#x4E0D;&#x62A5;&#x9519;&#x3002;</p>
<pre><code class="lang-javascript">v
<span class="hljs-comment">// ReferenceError: v is not defined</span>

<span class="hljs-keyword">typeof</span> v
<span class="hljs-comment">// &quot;undefined&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x53D8;&#x91CF;<code>v</code>&#x6CA1;&#x6709;&#x7528;<code>var</code>&#x547D;&#x4EE4;&#x58F0;&#x660E;&#xFF0C;&#x76F4;&#x63A5;&#x4F7F;&#x7528;&#x5C31;&#x4F1A;&#x62A5;&#x9519;&#x3002;&#x4F46;&#x662F;&#xFF0C;&#x653E;&#x5728;<code>typeof</code>&#x540E;&#x9762;&#xFF0C;&#x5C31;&#x4E0D;&#x62A5;&#x9519;&#x4E86;&#xFF0C;&#x800C;&#x662F;&#x8FD4;&#x56DE;<code>undefined</code>&#x3002;</p>
<p>&#x5B9E;&#x9645;&#x7F16;&#x7A0B;&#x4E2D;&#xFF0C;&#x8FD9;&#x4E2A;&#x7279;&#x70B9;&#x901A;&#x5E38;&#x7528;&#x5728;&#x5224;&#x65AD;&#x8BED;&#x53E5;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-comment">// &#x9519;&#x8BEF;&#x7684;&#x5199;&#x6CD5;</span>
<span class="hljs-keyword">if</span> (v) {
  <span class="hljs-comment">// ...</span>
}
<span class="hljs-comment">// ReferenceError: v is not defined</span>

<span class="hljs-comment">// &#x6B63;&#x786E;&#x7684;&#x5199;&#x6CD5;</span>
<span class="hljs-keyword">if</span> (<span class="hljs-keyword">typeof</span> v === <span class="hljs-string">&quot;undefined&quot;</span>) {
  <span class="hljs-comment">// ...</span>
}
</code></pre>
<p>&#x5BF9;&#x8C61;&#x8FD4;&#x56DE;<code>object</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">typeof</span> <span class="hljs-built_in">window</span> <span class="hljs-comment">// &quot;object&quot;</span>
<span class="hljs-keyword">typeof</span> {} <span class="hljs-comment">// &quot;object&quot;</span>
<span class="hljs-keyword">typeof</span> [] <span class="hljs-comment">// &quot;object&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x7A7A;&#x6570;&#x7EC4;&#xFF08;<code>[]</code>&#xFF09;&#x7684;&#x7C7B;&#x578B;&#x4E5F;&#x662F;<code>object</code>&#xFF0C;&#x8FD9;&#x8868;&#x793A;&#x5728; JavaScript &#x5185;&#x90E8;&#xFF0C;&#x6570;&#x7EC4;&#x672C;&#x8D28;&#x4E0A;&#x53EA;&#x662F;&#x4E00;&#x79CD;&#x7279;&#x6B8A;&#x7684;&#x5BF9;&#x8C61;&#x3002;&#x8FD9;&#x91CC;&#x987A;&#x4FBF;&#x63D0;&#x4E00;&#x4E0B;&#xFF0C;<code>instanceof</code>&#x8FD0;&#x7B97;&#x7B26;&#x53EF;&#x4EE5;&#x533A;&#x5206;&#x6570;&#x7EC4;&#x548C;&#x5BF9;&#x8C61;&#x3002;<code>instanceof</code>&#x8FD0;&#x7B97;&#x7B26;&#x7684;&#x8BE6;&#x7EC6;&#x89E3;&#x91CA;&#xFF0C;&#x8BF7;&#x89C1;&#x300A;&#x9762;&#x5411;&#x5BF9;&#x8C61;&#x7F16;&#x7A0B;&#x300B;&#x4E00;&#x7AE0;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> o = {};
<span class="hljs-keyword">var</span> a = [];

o <span class="hljs-keyword">instanceof</span> <span class="hljs-built_in">Array</span> <span class="hljs-comment">// false</span>
a <span class="hljs-keyword">instanceof</span> <span class="hljs-built_in">Array</span> <span class="hljs-comment">// true</span>
</code></pre>
<p><code>null</code>&#x8FD4;&#x56DE;<code>object</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">typeof</span> <span class="hljs-literal">null</span> <span class="hljs-comment">// &quot;object&quot;</span>
</code></pre>
<p><code>null</code>&#x7684;&#x7C7B;&#x578B;&#x662F;<code>object</code>&#xFF0C;&#x8FD9;&#x662F;&#x7531;&#x4E8E;&#x5386;&#x53F2;&#x539F;&#x56E0;&#x9020;&#x6210;&#x7684;&#x3002;1995&#x5E74;&#x7684; JavaScript &#x8BED;&#x8A00;&#x7B2C;&#x4E00;&#x7248;&#xFF0C;&#x53EA;&#x8BBE;&#x8BA1;&#x4E86;&#x4E94;&#x79CD;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF08;&#x5BF9;&#x8C61;&#x3001;&#x6574;&#x6570;&#x3001;&#x6D6E;&#x70B9;&#x6570;&#x3001;&#x5B57;&#x7B26;&#x4E32;&#x548C;&#x5E03;&#x5C14;&#x503C;&#xFF09;&#xFF0C;&#x6CA1;&#x8003;&#x8651;<code>null</code>&#xFF0C;&#x53EA;&#x628A;&#x5B83;&#x5F53;&#x4F5C;<code>object</code>&#x7684;&#x4E00;&#x79CD;&#x7279;&#x6B8A;&#x503C;&#x3002;&#x540E;&#x6765;<code>null</code>&#x72EC;&#x7ACB;&#x51FA;&#x6765;&#xFF0C;&#x4F5C;&#x4E3A;&#x4E00;&#x79CD;&#x5355;&#x72EC;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x4E3A;&#x4E86;&#x517C;&#x5BB9;&#x4EE5;&#x524D;&#x7684;&#x4EE3;&#x7801;&#xFF0C;<code>typeof null</code>&#x8FD4;&#x56DE;<code>object</code>&#x5C31;&#x6CA1;&#x6CD5;&#x6539;&#x53D8;&#x4E86;&#x3002;</p>
<h2 id="&#x53C2;&#x8003;&#x94FE;&#x63A5;">&#x53C2;&#x8003;&#x94FE;&#x63A5;</h2>
<ul>
<li>Axel Rauschmayer, <a href="http://www.2ality.com/2011/11/improving-typeof.html" target="_blank" rel="nofollow">Improving the JavaScript typeof operator</a></li>
</ul>




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